The one time I tried to introduce this was into a post-apocalyptic game set well over a millennia from now.

The idea was that an epidemic broke out and Britain was isolated by a disaster that separated most of the surviving land mass from the part connected to the European continent by the Euro Tunnel.

Thought to already be infected it was isolated and no one was the wiser until it was far too late.
The laboratories that experimented on animals were broken into and many of the lab animals released whatever process used mirrored that seen in the Rats of Nimm movie granting the surviving animals gradually increasing intelligence so eventually as most of humanity on the continent were wiped out by the various epidemics and the collapse of society.

This fledgling species I named "Anima" eventually found their way back to Britain now called Rhitia as refugees from the various wars plaguing the continent, the ones who reach Rhitia learned they could stay but only by swearing loyalty to the Archduke by that point the last remaining member of the royal family.

He was killed thwarting an invasion from a race of horrific barbarians calling themselves the Yuesha whose own continent was wiped out by a massive volcanic eruption forcing them to seek a new home on the other side of the world.

My game introduced the players who in their first game discovered the Archduke's tomb and the sister of one of the two nobles found and wore one of the raiments that acted as proof to claim the position of the Archduke.

Enter a pair of Meercat Anima based on a certain series of tv adverts (reversing the roles) and they recognised the symbol and sought her permission to settle properly as the Anima refugees were being forced to keep moving as the locals (including the ones responsible for telling them to seek the permission of the Archduke to settle) were taking every advantage they could as they were technologically more advanced than the bronze age surviving natives.

Surprised no one else tried the Rats of Nimm movie to encourage interest in this setting?

My favourite part was where they claimed they could summon reinforcements they started building a crude rocket.

Once they set up the fuse stretching a fair distance away from the rocket they put on protective gear and then when they lit the fuse they turned and ran until they dropped into cover a mile away!

The look on the players faces as they mentioned racing after them and then took cover as the rocket launched covering much of the distance between them and the rocket launching site in soot as the rocket streaked high up into the sky and blew up pretty much a rather over the top firework ultimately is why I remember it so well!

The last scene was a trio of airships launching WAY in the distance indicating the message had been received but players being what they are wasn't planning on staying put long enough for the reinforcements to arrive!

Had I managed to start the next session they were going to have to leave the Meercats behind as the terrain was becoming too much for their war chariot to cover but they'd encounter what I can only describe as a reptile sniper.

Still don't know whether she'd be friend or foe as I had a couple of pathfinder map sets ready for where they were heading to meet up with the bad guys.